The present invention relates to a hybrid inflator for inflating an inflatable vehicle occupant protection device, and particularly relates to a gas generating material for inflating an inflatable vehicle occupant protection device.
A hybrid inflator for inflating a vehicle occupant protection device includes a quantity of a stored gas and a gas generating material. The stored gas typically comprises an inert gas and an oxidizer gas. The oxidizer gas helps to support the combustion of the gas generating material. An igniter is actuatable to ignite the gas generating material. As the gas generating material burns, it generates heat and a volume of combustion gas. The heat and combustion gas increase the pressure of the inert gas. The heated inert gas and combustion gas form the inflation fluid. The inflation fluid is directed into the air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
U.S. Pat. No. 5,125,684 discloses a gas generating material for use in a vehicle occupant restraint system. The gas generating material comprises cyclotetramethylenetetranitramine (HMX) or cyclotrimethylenetrinitramine (RDX), an oxidizer salt, and a cellulose based binder. The advantage of using the cellulose based binder in the gas generating material formulation is that the cellulose based binder produces a low-level of carbon monoxide upon combustion compared to conventional polymeric binders.
Cellulose based binders are generally resistant to oxidation and degradation at atmospheric pressure. It has been discovered, however, that cellulose based binders oxidize and degrade, over time, when stored in a high pressure oxygen rich atmosphere (e.g., an atmosphere with a pressure greater than 1,000 psi and a concentration of oxygen greater than 10% by weight). Free radicals of oxygen in a high pressure oxygen rich atmosphere oxidize the chemical double bonds of the cellulose based binder. The oxidized bonds cleave and cause the polymer chain of the cellulose based binder to fragment.
The present invention is an apparatus for inflating an inflatable vehicle occupant protection device. The apparatus comprises a container for storing a supply of gas. A gas is stored in the container at an elevated pressure. The gas comprises an oxygen rich oxidizer gas. A gas generating material is stored in the container and is exposed to the oxidizer gas at the elevated pressure. The gas generating material comprises a cellulose based binder blended with an anti-oxidant material. An igniter is provided for igniting the gas generating material.